The status of laser ionization schemes at ISOLDE’s RILIS and the
scope for improving efficiencies
Thomas Day Goodacre
1st LA³NET Topical WorkshopLaser Based Particle Sources
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Reasons for Scheme Development for ISOLDE’s
RILIS
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The addition of new lasers to the RILIS at ISOLDE necessitates a re-evaluation of the current ionization schemes:
• Have existing schemes been adversely affected or can they be improved upon?
• Are new elements now accessible?
This talk will explore:
• The principles of ionization scheme development
• Elements of particular interest for re-evaluation
• The equipment and methods available for scheme development
Reasons for Scheme Development for ISOLDE’s
RILIS
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New Laser Setup
The previous RILIS laser setup consisted of 3 dye lasers pumped by 2 copper vapour lasers.
Fedosseev et al. 2012
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Resulting Wavelength Range
200 300 400 500 600 700 800 900 10001
10
100
1000
10000
100000
TiSa FHG Dye THGUV-pumped Dye SHG Dye SHGTiSa THG TiSa SHGUV-pumped Dye Fundamental Dye FundamentalTiSa fundamental
Wavelength, nm
Pow
er, m
W
Fedosseev, V. N., Fedorov, D. V, Fink, D., Losito, R., Marsh, B. A., S.Rothe et al. (2012). Upgrade of the RILIS at ISOLDE; Rev. Sci. Inst 83(2), 02A903. doi:10.1063/1.3662206
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Viable Schemes at ISOLDE’s RILIS
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Goal of Ionization Scheme Development
To find the most efficient method of ionisation whether by:
• Exciting to the continuum
• Exciting an autoionizing resonance
• Ionization from a Rydberg level
Image by V.I. Mishin
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Factors Affecting Scheme Efficiency
Scheme efficiency is determined by a number of things:
• Transition strengths
• Statistical weights (J value)
• Thermally populated lower levels
• Width of the resonance or splitting of the lines (hyperfine structure)
• Photon flux (up to saturation)
• Laser pulse duration Vs Lifetime of excited levels
Technical aspects also affect efficiency:(laser pulse synchronization, delay, overlap, beam transport efficiency, stability, reliability)
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Potential Scheme Developments for ISOLDE’s RILIS
The scope for ionization scheme development for ISOLDE’s RILIS falls into five categories:
1. Feasible but a suitable ionization scheme has yet to be developed: Cr, Se, Te, B, Ra, La, Ce, Pm, Er
2. RILIS enhancement low due to surface ionization, so needs an efficient scheme and/or surface ionization suppression:
K, Cs, Li, Na, (Ba), (Ra)
3. Existing scheme using non-resonant ionization for the final step, AIS desired: Mg, Sc, Co, Zn, Ga, Y, Ag, Cd, In, Sb, Tl, Pb, Bi, Po, At, Dy
4. Suboptimal schemes or laser configurations:Hg
5. Refractory metals, requires further development of targets and ion sources:V, Zr, Nb, Mo, Ru, Rh, Ta, W, Re, Os, Pt, Ar, Pa
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Basic Formula for Scheme Development
1. Literature search and use of databases (Kurucz and NIST) to determine resonant steps.
2. Resonance ionization spectroscopy Laser frequency scans across regions of interest whilst
observing the ion current
3. Saturation measurementsDetermine if efficiency gains can be achieved from an increase of power.
4. Efficiency measurementsTotal evaporation of the sample (of known mass) and
integration of the ion current.
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Methods of Ionization Scheme Development for
RILIS 1Dedicated off-line experiment using a target and mass marker- Enables optimization of RILIS specific parameters - Efficiency can be measured- Requires dedicated separator use + target preparation and setup (limited to 1-2
weeks/yr)- Limited to stable isotopes
Images from Julien PARRA-LOPEZ
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Methods of Ionization Scheme Development for
RILIS 2Dedicated on-line experiment using a target and radiogenic isotopes:
- The only method for scheme development of exclusively radioactive isotopes (Po, At)
Cocolios and Marsh et al. 2008
Po
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Methods of Ionization Scheme Development for
RILIS 3Opportunistic scheme development during an on-line RILIS run:- Use any available tuneable laser to search for alternative ionization
schemes (e.g. Ca)- Only possible due to the Dual-RILIS set-up- Time and laser availability limits the scope of this method.
Daniel Fink PhD work
Factor of 4 improvement!
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Methods of Ionization Scheme Development for RILIS 4
Scheme development using an independent reference cell- A thermal atomic beam unit, developed by Tobias Kron at the University of Mainz will
be installed in the RILIS room scheme development for stable elements using the RILIS lasers.
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Schemes of InterestPriorities are governed by ISOLDE user requests or the degree of potential interest:
4
2
11
3
2
1
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Schemes of Interest
Efficiency ≈1%
Low efficiency because of a weak first step and power had to be split between 3 dye lasers.
AIS was reached using the fundamental output of the 2nd step dye laser
1st step Ti:Sa then 2 independent dye lasers
Saturate transitions
Locate peak of the AIS
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Hg – 2 stages
• 1st step provided by a frequency tripled Ti:Sa laser• Dye laser for the 2nd step will require ~30 W of the ~90 W Edgewave pump power. • ~ 60 W pump power available for second dye laser to scan across the region of the AIS.
600-675 nm
Investigate the ionization schemes and AIs identified by Podshivalov et al. 1999.
1)
2)
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Development at LARISEquipped for:• Atomic or molecular spectroscopy, • Determination of ionization potentials and
hyperfine structure measurements of stable isotopes.
Three tunable lasers operating at 10 Hz:• Nd:YAG pumped dye laser• 2nd harmonic Nd:YAG pumped OPO• 3rd harmonic Nd:YAG pumped OPO• 3 frequency doubler/tracker units• Frequency tripling without tracking.
Two complimentary atomic beam sources:• Rotating rod laser ablation source with gas
extraction and TOFMS -refractory elements.• Tantalum oven atom source with residual gas
analyser and TOFMS.
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Development at LARISOn going work at the LARIS lab:
• Development of ionisation schemes for Zr and Hf atoms + molecular breakup of fluorides (Nobu IMAI)
• Plan for scheme development of Nd in collaboration with LAL at ORSEY for enrichment.
• Scheme Development of Ba
• Scan an autoionizing resonance identified by M.A. Kaylar et al. 2009.
• First step frequency doubled dye
• Fundamental of the OPO for the Second
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Summary
Additional lasers allow for old schemes to be re-evaluated and new ones developed
Development will take place at both ISOLDE’s RILIS and in the LARIS lab
Priorities for development are determined by user requests
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Collaboration for Scheme DevelopmentRILIS elements database developed by Martin Klein and
Sebastian Rothe:
The idea of this database is to be a communal resource for all RILIS (not just ISOLDE’s) schemes.
In addition to inputting successful schemes there is the hope that unsuccessful AIS searches could be recorded in the notes: saving everybody’s time!
Fully functional but still in the testing phase so recommendations are more than welcome!
http://riliselements.web.cern.ch/riliselements/index.php
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Acknowledgements
Thank you for your attention!
Valentine FEDOSSEEV1, Daniel FINK1,2, Nobuaki IMAI3, Tobias KRON4, Bruce MARSH1, Ralf Erik ROSSEL5, Sebastian ROTHE1, Maxim SELIVERSTOV6,
1CERN2University of Heidelberg3KEK, Japan 4Hochschule Rhein Main, Wiesbaden5Johannes-Gutenberg-Universitaet Mainz6Petersburg Nuclear Physics Institute (PNPI)